A piezoelectric/electrostrictive actuator has an advantage that its displacement can be precisely controlled in a submicron order. Especially, a piezoelectric/electrostrictive actuator using a sintered object of piezoelectric/electrostrictive porcelain composite as a piezoelectric/electrostrictive object has a further advantage that its electromechanical transduction efficiency is high, its generated force is large, its response speed is quick, durability is high, and its power consumption is low, in addition to the advantage that a displacement can be precisely controlled, and is adopted as an ink-jet head and a micro pump, etc. taking advantage of these advantages.
However, in the art, there has been a concern about degradation and an insulation breakdown of a piezoelectric film (piezoelectric object) in high temperature and high humidity conventionally, various measures have been taken in order to suppress such degradation and an insulation breakdown of a piezoelectric film due to water.
For example, patent document 1 (PTL 1) describes that by disposing an electrode with a low rate of moisture vapor transmission rate on a piezoelectric film, and disposing a protective film which consists of inorganic material covering a peripheral part of the electrode and piezoelectric film, invasion of moisture to the piezoelectric film can be prevented.
Moreover, patent document 2 (PTL 2) describes that the thickness of the insulating layer formed only by electrodepositing and baking (electrodeposition coating) acrylic paint etc. on an outer periphery a laminated electrostrictive actuator is insufficient and therefore invasion of moisture from the corner part can be suppressed by performing second electrodeposition coating anew after the electrodeposition coating of the paint.
Further, patent document 3 (PTL 3) describes that by coating a piezoelectric element for ink-jet heads which has a minute crack generated at the time of slicing processing with epoxy adhesive to fill up the minute crack therewith and thereafter drying and hardening the epoxy adhesive, the strength and moisture-proof property thereof can be improved.
Furthermore, patent document 4 (PTL 4) describes that by coating the exposed part of an internal electrode layer and an exterior electrode in laminated type piezoelectric ceramics with silicone, hardening the silicone to form an exterior part, migration of electrode material and a short-circuit can be prevented.